TCU and 4L80e quesitons

[critter]

I'll try to make a long story short.

The car is a 1974 Pontiac Trans Am. Motor is a 462ci Pontiac. Transmission is a 4L80e that shows a 1997 tag but has the 2 cooler line ports together at the front. It's a GM Goodwrench rebuild from the looks of that tag that I found on top of the transmission. It was a used transmission sold to me as a working transmission.

We installed the transmission and it was slipping badly in all forward gears. Pulled it back out and went to a shop. All the steels and clutches were toasted. It has now been rebuilt and and reinstalled. All lines and the converter were flushed before reinstalling.

Today we tried to drive it. It did seem to drive with positive engagement once we got the right amount of fluid in it but it's not shifting correctly. I'm going to 3000 rpm before I see a shift. I do have the TCU file and a datalog if anyone wants to see it. I've already sent that to Chris Robbins at TCI for his input.

One thing I notice in the data log is that the TCU doesn't seem to see a smooth, linear TPS input. It seems spikey. Could that be the linkage? I'm using a factory Quadrajet and a home grown linkage so that's why I ask. Any other thoughts are welcome.

[critter]

I've been reading the instructions for the TCU again this evening. I see where it says the base voltage reading on the TPS should be in the .4 range. I think mine was at zero. That might explain a few things.

Critter,
Is this a red box or a gray box? Also Please send me that Datalog and tcu file. The TPS has to be spot on for thing to work properly if its a red box you need to have above 0v at idle and below 5v at WOT. If its a grey box you need to have .4-.5v at idle and 4.5-4.6 at WOT. Please email or call me and i will be more thna willing to help you out.

[critter]

It's the red one, made by FAST. I think the part number is 377500.

I'll email you the stuff. Thanks.

I will wait for the email and go from there.

Thanks

[critter]

The frustration level has hit 10. Even after triple checking the TPS voltage and reprogramming the TCU it's still slipping and not shifting. The fluid is starting to have a slight burned smell again. No more driving it for data logging. I'm about to put that TH400 back in it. I can't afford another transmission rebuild.

I'll send in the data log I made from tonights drive tomorrow but it appears to me that the TCU line pressure DROPS when TPS voltage goes up. Am I reading this incorrectly? The value is 60 at idle and goes down on that gauge as RPM and TPS voltage increase. I don't understand.

This appears for all the world like a low pressure situation. The car goes solidly in to gear in reverse and drive. You can take your foot off the brake and it move just like you'd expect. As soon as I apply throttle it begins to slip and it never shifts out of first gear.

HELP!

The frustration level has hit 10. Even after triple checking the TPS voltage and reprogramming the TCU it's still slipping and not shifting. The fluid is starting to have a slight burned smell again. No more driving it for data logging. I'm about to put that TH400 back in it. I can't afford another transmission rebuild.

I'll send in the data log I made from tonights drive tomorrow but it appears to me that the TCU line pressure DROPS when TPS voltage goes up. Am I reading this incorrectly? The value is 60 at idle and goes down on that gauge as RPM and TPS voltage increase. I don't understand.

This appears for all the world like a low pressure situation. The car goes solidly in to gear in reverse and drive. You can take your foot off the brake and it move just like you'd expect. As soon as I apply throttle it begins to slip and it never shifts out of first gear.

HELP!

The line pressure number is the pulse width on the solenoid so as the number goes down line pressure comes up. Anyhting about 80% throttle should be at 0 on that scale. I will be sure to have Chris call you.

[critter]

Just to follow up this thread, Chris did contact me by phone and has gone over the data logs with me. He says it appears the TCU is doing what it should but he has tweaked the TCU file for me. I'll upload that when I'm back in the shop.

The transmission builder insists that this is a TPS issue, even though the TCU is seeing the voltage. I asked another builder who specializes in performance 4L80e transmissions. He's asking me to run figures with a pressure gauge because he suspects pump problems, even though it has been rebuilt.

My plan is to double check the hook up of the wiring harness and then hook up the gauge and run his recommended test for line pressure. Then I'm going to replace the TPS, TISS and TOSS.

[critter]

The gauges showed no pressure in P, D and 50 psi in R.

I unhooked the computer and had 150psi and 300psi respectively.

I have electronics issues. I need someone who can email me the pin outs of the harness so I can Ohm it out and check for broken wires. Anyone got that. I see something in the TCI instructions but I'd like something that's more readable and I can print out. Russ?

I will be calling you shortly.